The proposed work involves the structural studies and sequence analysis of biologically important regions of three members of human adenovirus DNAs from serotypes 2, 7 and 12 which are non-, weakly or highly oncogenic serotypes, respectively. First the inverted terminally repetitious region, a unique structural feature, commonly shared by all the serotypes so far tested, will be sequenced. This region is probably biologically important because it has been shown to be a portion of the transforming segment of the DNA which has been characterized in other laboratories in at least three adenovirus serotypes 2, 7 and 12. The purpose of this work is also to find a correlation, if any, between the length of this region and its nucleotide sequence homology to the oncogenic potential of some important adenovirus serotypes. During the course of this work in our laboratory, some interesting aspects of the structural uniqueness in adenovirus serotype 2 were discovered. A protein of MW 55,000 daltons is covalently attached at or near the 5' ends of adenovirus 2 DNA. Further studies on the biological significance of the tight binding of a protein at the two ends of Ad 2 DNA are under progress in view of the fact that the origins of DNA replication have been located near the two termini.